Effect of compaction water content and stress ratio on permanent deformation of a subgrade lateritic soil

Abstract

Permanent deformation is a potential distress that affects the functional characteristics of pavement. Subgrade soil might contribute to different levels of permanent deformation depending on traffic intensity. This paper assesses the stress ratio effects as well as compaction water content variation on permanent deformation of subgrade soil, presents some contributions to understanding the Shakedown concept in fine-grained soils and evaluates models for estimating soil plastic strain. Repeated load triaxial (RLT) tests were performed on lateritic sandy soil in order to obtain: permanent deformation and Shakedown parameters. Findings indicated a prevalence of stress ratio in permanent deformation for a specified compaction water content range (wopt ± 1.5%). However, analysis of plastic strain rates showed that permanent deformation might be more influenced by compaction water content than by stress ratio, mainly in cases where compaction water content range is wider. Furthermore, stabilization, i.e. Shakedown first phase occurrence, was achieved under all test conditions, in spite of low deformation levels. Lastly, the model adjusted in function of stress ratio and compaction water content closely represented the complexity of soil plastic strain accumulation.